350 marine engine rebuild help needed

I need to rebuild an engine in my Mastercaft boat. It has 1200h, which is A LOT for a boat engine (boat engines live a very tough life: a combination of high load and high RPM is what ultimately kills them).

Mastercraft uses marinized SBC 350 engines made by Indmar, with the following specs:

- 1 piece rear main seal
- engine block casting number 880
- vortex heads (170cc?)
- center bolt valve covers
- 8-bolt intake manifold
- plastic timing cover

https://boats-from-usa.com/sites/def...15-1199275.jpg

The engine has multipoint fuel injection (it runs in an open loop, unlike road engines, which have closed loop systems with lambda sensors), Indmar ETX exhaust headers and is rated at 350hp (may be a bit optimistic, but that is what they claim).

Anyway, I have to rebuild that engine since it just died. I have seen a complete engine rebuild kits with marine gaskets etc on ebay for ~ $400.

Since those kits look to be assembled from pretty standard parts, I was wondering, if pouring $400-600 extra on some performance parts would make the engine last longer ?

If I could increase the RPM potential of that engine from max recommended 5000 RPM to 5500 RPM - all the better.

Is so, what would you recommend ?

Performance bearings ? Timing chain ? Valve springs ? Other ?

build bottom end power and torque do you can pull a bigger prop instead of higher rpm . gm valve trains dont like high rpm .

Two problems with that solution:

1. This is a tow boat (for surfboard and wake board) not a regular boat. I have wake/surf optimised propeler. When I tow, I have over 3000lbs of ballast (water) onboard. With such a load, and a couple of ppl onboard, the boat wouldn't probably even go past 4800 RPM.

However, when I drain the ballast, making the board much lighter, I can easily reach 5000+ RPM. That is when I would like to have some extra headroom.

2. Stroking the engine to make more tq down low, would require ECU reprogramming (same for and head job, new camshafts etc), which I'm not able to do. This is a marine multipoint fuel injected engine (that runs an open cooling system, throwing water out via the exhaust), so I cannot even put it on a chassis dyno, not to mention the regular rolling road dyno.

So I'm basicly stuck with the factory ECU tune - I can only rev it higher.